Conditions InDepth: Endometriosis

Endometriosis is a problem with the lining of the uterus (womb). The lining is called the endometrium. Normally, when you have your menstrual period every month, the lining will come out in the menstrual flow through the vagina.

Endometrial tissue is normally found only inside of the uterine cavity. However, endometriosis refers to the presence of the endometrial tissue outside of the uterus. The most common sites include: the ovaries; the outside surface of the uterus; the fallopian tubes; ligaments of the pelvis; and the spaces between the rectum, bladder, and uterus. Less commonly the rectum, bladder, intestine, and appendix may be involved. Rarely, deposits (or implants) of endometrial tissue may be found in the lung, arm, thigh, and skin far away from the reproductive tract.

This misplaced endometrial tissue responds to the monthly cycles of reproductive hormones. It swells, breaks down, bleeds, and causes an inflammatory reaction. Whereas during the normal menstrual flow the blood exits through the vagina, there is no exit when this tissue is in other locations outside of the uterus. The pain is increased during the latter part of the menstrual cycle and the beginning of menses.

In the United States, endometriosis affects an estimated 10%-20% of women of reproductive age. Although endometriosis may occur at any age, it is most commonly seen between the ages of 25 and 40.

The exact cause of endometriosis is unknown. Some possible considerations include:

Menstrual blood and endometrial tissue flows backward through the fallopian tubes instead of forward through the vagina and out of the body.

The immune system does not destroy this misplaced tissue in the body and allows the tissue to implant and develop in unusual places in the body. This causes endometriosis.

The lymph (glands) and/or blood systems carry endometrial cells from the uterus to other areas of the body.

Genetic and environmental susceptibility.

Endometriosis is a major factor in female infertility. In fact, about 30%-45% of all women who are being treated for infertility have evidence of endometriosis.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.